The invention relates to the telecommunication field and, more particularly, to a service message system for a switching architecture that includes at least one Switch Fabric with a switch core located in a centralized building, and a set of SCAL elements distributed in different physical areas for the attachment to the different Port adapters.
Modern switching architectures tend to become more and more complex and fast. Complexity may be expressed in terms of number of individual switching modules and the number and speed of the Terminal Adapters that may be attached to the switching architecture. Different ways are provided for aggregating modern switching modules and expanding their performance for providing the high-speed switches that are required. The switches may be expanded in terms of the number of ports and the speed of a given technology. Shared buffer switches can be more enhanced by means of speed expansion and port expansion mechanisms, and even buffer expansion. Examples of such shared buffer techniques can be found in the non published
As the degree of sophistication of the switching architecture increases, it is highly desirable to provide strong and efficient possibilities of testing, maintenance and fault tolerance capabilities at every particular location within the architecture, even when the latter expands over some hundreds of meters. Therefore, it is very important that the switching architecture is fitted with some appropriate and effective service message capabilities. The service message should permit an effective possibility of control message transmission so as to permit a safe switch-over of some components when this appears necessary, particularly when a maintenance operation is planned. Additionally, the service message channel should enhance the possibilities of testing the different parts of the system, particularly when the latter is very large and complex because of the use of a port expansion architecture.
It is an object of the present invention to provide a simple and efficient service message channel that is adapted to the topography of the modern switching architectures, comprising numerous different components.
It is a further object of the present invention to provide a service message that suits the needs of breakdown detection that is required in the large switching architectures based on port expansion.
It is another object of the present invention to provide a service message capability that permits an easy switch-over process between two particular Switch Fabrics that are mounted in a fault tolerance arrangement.
These and other objects of the present invention are achieved by the service message system for a switching architecture that is defined in the set of claims. Basically, the switching architecture includes at least one Switch Fabric comprising a switch core located in a centralized building and a set of Switch Core Access Layer (SCAL) elements distributed in different physical areas for the attachment to the different Port adapters. Each SCAL element particularly includes a SCAL receive element and a SCAL Xmit element for the respective access to one input port and one output port via serial links. The service message is based on the use of a Cell qualifier field at the beginning of each cell, which comprises a first and a second field. The first field is the Filtering Control field which permits an easy decoding of a service message cell, when applicable. The second field is used for determining which particular type of service message is conveyed via the cell. Following the Cell qualifier is the Switch Routing Header (SRH) which permits the characterization of the destination of the cell and is used for controlling the routing process.
Preferably, the service message is used in a fault tolerance configuration where two different Switch Fabrics act as a standby to each other and share a part of the traffic: each one is configured as a default routing path for some port adapters and a backup path for the others. In that particular configuration, the service message of the invention uses the first field of the Cell qualifier to transport a Direct filtering command causing the Switch fabric to route the cell when the SRH is representative of its default output port destination. Conversely, the first field may transport a Reverse filtering command in the first field that causes the Switch fabric to reverse the default routing process. The first field is also used for characterizing a service message cell which the second field indicates the accurate type. Particularly, two types are used for the production of the filling cells when no data cell is to be transmitted at a particular location of the switching architecture.
Preferably, in response to a detection of an error condition or a switch-over request for maintenance purpose, each SCAL Receive element generates filling cells of said second type instead of the filling cells of said first type when this is necessary, i.e., when no data cells are to be transported. Similarly, each switch core starts producing filling cells of the second type in lieu of filling cells of the first type when all the input ports receive filling cells of the second type. This permits propagation on the switch core the limit of flow of data cells. When each SCAL Xmit element receives the filling cell of the second type, it can uses the latter as an indication that a safe switch-over can be achieved, without loss of cell, disordering of sequence, etc.
In a preferred embodiment of the invention, the service message is used in association with the port expansion architecture. In that situation, several switch cores are mounted in a port expansion configuration via corresponding Fan-out and Fan-in circuits. Each SCAL Receive element regularly uses the service message channel for producing cells of a third type which are received by the corresponding switch core attached at the opposite end of the serial link (of several hundreds of meters) for performing a test continuity and analysis of the input segment of the port expansion architecture comprising the fan-out circuit. More preferably, the detection is made by means of hardware circuits, thus requiring no huge amount of processing resources and the result of the detection is reported into a 16-bit register that the processor inside the core may access to get a precise status of all the input ports.
Similarly, the Switch cores regularly produce service message cells having a still different type than the preceding ones, and which are received by the corresponding SCAL Xmit element in order to test the output segment of the port expansion architecture comprising the fan-in circuit. In a preferred embodiment of the invention, the port expansion factor is fixed to 2 and the number of fan-in circuits is two. Therefore, each branch located upstream the fan-in circuit is assigned an unique type of service message cell, which permits very accurate and effective breakdown detection.